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GPS: A military perspective

Rajat Baijal
Rajat Baijal

Manoj K. Arora
Manoj K. Arora
Department of Civil
Engineering IIT Roorkee
Roorkee 247 667
manojfce@rurkiu.ernet.in


Abstract
Accurate and todate information on the location of enemy and own forces is one of the most critical information a military commander seeks. In today’s fast paced electronic battlefield such information if disseminated timely can act as a major force multiplier. The dawn of the space age has led to the development of several dual use technologies, which find extensive application both in military and civilian fields. Global Positioning System (GPS) is one such technology. Military forces the world over are using GPS for diverse applications both during wartime and peacetime. These include navigation, targeting, rescue, guidance and facility management. With war clouds looming over west Asia, the US led forces are likely to showcase weapon systems, which rely heavily upon GPS for their accuracy and lethality. In this paper, some applications where GPS can be used effectively by the armed forces, have been highlighted.

Introduction
Human beings have always looked towards the skies for navigation. Till today celestial bodies like sun and stars are used for finding out the directions. This assumes more importance if you are a soldier moving in unknown enemy territory. The significance of locating one’s position in the world cannot be more important than for a soldier, as this could mean the difference between life and death, defeat and victory.

With the coming in of the space age, mankind has tried to replace these celestial bodies with artificial satellites so that navigation is possible both during day and night. Global Positioning System (GPS) is one such dual use technology, which has found extensive application both for military and civilian purposes in area of navigation and others. GPS has given military forces the lethal combination of precision strike with adverse weather performance, standoff range, and operational flexibility - all at a low marginal cost (Hasik, 2001).

Origin of GPS
The Navigation Satellite Timing And Ranging (NAVSTAR) GPS was developed by the US Department of Defense (DoD) as a worldwide navigational and positioning resource both for military and civilian uses. The system is based on a constellation of twenty-four satellites in six orbits (Fig 1) acting as reference points for receivers on ground (Hurn, 1993).

Requirements of a Good Navigation System for Military
The basic needs of any armed forces as far as a good navigation system is concerned can be enumerated as below.
  • Accurate
  • All Weather
  • Easy to use
  • Portable
The GPS system currently in service meets these requirements fully except for the fact that ultimately it is a system run for the US military and if you happen to be their adversary then you may be in some problem as the power to introduce intentional error in the signal rests with them. Although the US DoD’s policy of “Selective Availability” (under which intentional noise was added to GPS signals to make them less accurate) has been removed last year, its reintroduction is still in their hands.

Accuracy of GPS may vary from few meters to few tens of meters, which meets the military needs for navigational purposes. However, for precise location of targets for aerial bombings, missile strike etc accuracy to a level of mm is required. This can be achieved through Differential GPS (DGPS). Nevertheless to achieve this level of accuracy, proper error modeling is necessary. A detailed discussion on GPS related errors and accuracy may be found in Tiwari et al. (2000).

Further, the GPS satellite signals are also not affected to that extent due to bad weather as conventional terrestrial radio signals. This is an important requirement, as military forces need all weather navigation systems.

Most of today’s GPS receivers are quite easy to use and give the position in both the geographical latitude and longitude and the local map projection system coordinates besides providing data in WGS-84 coordinate system. Moreover over the years, the GPS receivers have also drastically reduced in size and weight, and thus become more portable. For example, today wristwatches commercially available off the shelf have GPS receivers built in them.


Fig.1: Image showing orbits of various GPS satellites
(Source: http://www.gps4fun.com/home.html)

Military Applications of GPS
The role of the military in any country can be very varied and every system for it must meet these requirements fully. In general, there are two major tasks of the military vis Barrack and the Battlefield. Barrack encompasses all the peacetime activities in which the military personnel are involved. This may include training, disaster relief, peacekeeping and management of large bases / installations. Battlefield includes all wartime activities. The military applications of GPS revolve around these activities. Some of these can be enumerated as,
  • Navigation
  • Tracking
  • Bomb and Missile guidance
  • Rescue
  • Facility Management
  • Map updation
These are only some of the applications as more and more uses may be derived from GPS.


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